Photocuring device with axial array of light emitting diodes and method of curing

ABSTRACT

A device for curing a photosensitive dental composition curable by way of irradiation with light of predetermined wavelength includes a power supply; and a radiation source coupled to the power supply and powered thereby, the radiation source having a radiation output and including an axial array of light emitting diodes. The light emitting diodes are mounted about an assembly axis defined thereby at a plurality of axial distances from said radiation output of the radiation source and being further characterized in that the plurality of light emitting diodes are directed along a plurality of divergent paths such that a position insensitive optical field is generated for curing the dental composition.

TECHNICAL FIELD

The present invention relates generally to photocurable dentalcompositions and more specifically to a device provided with an axialarray of light emitting diodes directed along a plurality of divergentpaths such that a position insensitive optical field is generated.

BACKGROUND

Certain polymeric materials useful in the field of dentistry foradhesion, sealing and restoration may be cured or hardened upon exposureto a source of radiation. Such photoactive materials are known as“photo-curable dental compositions” and generally harden when exposed toradiation having wavelengths in the visible range. Photo-cured dentalcompositions are convenient for use by a dentist because the curingprocess can be initiated when the dental composition has been accuratelyplaced in its proper position. A source of radiation energy positionedproximate to the material to be hardened, for example an appropriateamount of composition placed inside a tooth cavity, is activated toinitiate polymerization and subsequent curing of the composition tosecure the repair. Early methods for curing photosensitive dentalcompositions included dental guns and other apparatuses for producingconcentrated beams of UV radiation. See U.S. Pat. Nos. 4,112,335 and4,229,658, for example. Later, visible light curable dental compositionswere used and dental radiation guns for producing concentrated visiblelight were provided like that disclosed in U.S. Pat. Nos. 4,385,344 and6,171,105. However, a relatively high divergence about 25 degrees of thelight beam from such visible light sources reduces penetration into thetooth structure, leading to their relative inefficiency andunreliability for photo-curing dental composition that are thicker thanabout two millimeters.

Photo-curable dental materials have also been developed that arehardened by exposure to radiant energy in a pre-selected spectral range.Typically, a photo-activated chemical reaction in many photo-curabledental materials is initiated by application of a high intensity bluelight having a wavelength of 400-500 nanometers. Since the light sourcesemployed typically produce the entire visible light spectrum as well assome non-visible radiation, a reflector is coated to reflect onlyvisible light, and the filters are selected to substantially blocknon-visible radiation and visible light other than blue light in therange of 400-500 nanometers, in order to produce the desired range ofradiation, as shown for example in U.S. Pat. No. 5,147,204. Other highpower arc sources, such as the one disclosed in U.S. Pat. No. 5,879,159,produce filtered wavelengths in the 430-505 nanometer range. Laser basedradiation sources have also been employed, using for example, anargon-ion laser producing either specific wavelengths or theircombinations in the 450-514 nanometer range. See U.S. Pat. No.5,616,141. U.S. Pat. No. 6,099,520 discloses a portable, cordless,hand-held device that uses a diode-pumped microchip laser emittingradiation at 480 nm.

There are several disadvantages in using light curing apparatuses of theprior art like those discussed above. Commercially available dentallight guns that use metal halide or plasma ark lamps often include anelongated, slender light guide such as a bundle of optical fibers havinga free end that can be positioned close to the photo-curable material inorder to direct light to the material from a light source locatedoutside the oral cavity. The bundle of optical fibers is an addedcomponent that reduces the efficiency of the light reaching the curingsite. Thus, because of the relatively large size of the dental gunwithin a patient's mouth, a degree of physical discomfort is introducedto the patient as well as to the dentist who must hold the gun steadyfor about one minute. These sources produce all visible and somenon-visible wavelengths and use band pass filters to admit wavelengthsof interest. The result is a heating of the device that must be cooledusing a cooling fan or other means.

Second, the area illuminated by conventional blue-filtered metal-halideradiation is usually in the range of about a ½-inch diameter circle andover a typical curing cycle of about 60 seconds. The relatively highenergy output and beam divergence of such dental guns leads to thepossibility of increased heating of the pulp tissue which is sensitiveto small changes in temperature.

The argon laser sources are bulky and transport of laser light from theargon laser source to the curing site can only be accomplished by a longfiber-optic delivery system. The technology of either the argon laser orthe diode-pumped microchip laser is complex and prevents inexpensiveimplementation. Their maintenance and repairs are also expensive Lasersare intrinsically inefficient devices meaning that a very small portionof the electrical energy is finally converted to useful light.Furthermore there is the danger of accidental exposure of coherent laserradiation to the eye of either the dentist or the patient during thedental procedure resulting in a damage that could be greater than thatresulting from incoherent radiation.

In addition, when dental compositions are cured in place within a cavityfor instance, after curing an amount of shrinkage of about 2.5-3.0%occurs leaving a gap within the area being treated; such shrinkage is sodeleterious that any small reduction in shrinkage is desirable.

Furthermore, in tests of cure depth uniformity of standardizedcompositions, it was found that a high percentage (46%) of curing lightsused in private dental offices are unsuitable for use when testedagainst manufacture's recommendations using a curing radiometer or aheat radiometer, due in part to the loss of output of the light sourcein use [J Dent Mar. 27, 1999 (3):235-41]. Finally, due to the expensesof combining a laser or metal-halide radiation source, focusingelements, power sources, etc., significant expense are involved inpurchasing and using dental guns. Conventional dental curing devices aretherefore seen to have shortcomings including uncomfortable use,unreliable curing and relatively high expense.

U.S. Pat. No. 4,385,344 discloses a dental gun device for production oflight in the low visible range for photo-curing dental compositions, thedevice comprising a tungsten halogen lamp with a concentratingreflector, which reflects visible light and passes middle and farinfrared wavelengths. A dichroic heat reflecting filter which passeslight from 400 to 700 nm and reflects energy in the visible red and nearinfrared wavelengths back to the lamp envelope, enhances lamp halogencycle efficiency. The dichroic heat-reflecting filter is followed by adielectric filter, which provides a high efficiency bandpass at thedesired visible range. A fiber optic light guide is positioned toreceive the focused and filtered light and to transmit it to a reducedsurface light-applying tip at the end of the handpiece. The fiber lightguide is encased in a specially designed sheathing, which providesprotection to the optical fibers and carries two electrical conductorswhich are connected between a control switch on the handpiece and thepower supply for the lamp.

U.S. Pat. No. 5,147,204 is representative of conventional blue-lightfiltered dental guns. This patent discloses a blue light emittingapparatus for curing photo-curable dental material including a handpickhaving a housing, a depending handle and a detachable light guide. Thelight guide is received in a head connected to the housing. A source oftungsten-halogen light is coupled to the housing, and a light guide isdetachably connected to the head for communication with the source oflight. Since the tungsten-halogen light produces the entire visiblelight spectrum as well as some non-visible radiation, a reflector iscoated to generally reflect only visible light, and a blue-pass filterand a heat filter are selected to substantially block non-visibleradiation and visible light other than blue light in the range of400-500 nanometers.

Still further devices and techniques have been proposed as noted below.

There is shown in U.S. Pat. No. 5,420,768 to Kennedy, for instance, aportable photo-curing device that has a light emitting diode matrixwhich is energized with battery power. The '768 patent notes in Column 2that LEDs of various selected colors may be formed on the module byusing selected color dyes so that the emitted light is a pure whitelight or a combination of selected color lights to provide apredetermined photo curing effect. The light emitted by the LEDs mayhave a peak wavelength of 470 nm which is used for photo curingpurposes.

U.S. Pat. No. 5,634,711 to Kennedy et al. discloses a portable lightemitting device suitable for medical and industrial photo curing. It isnoted in the '711 patent that various applications require differentlight dosage values. For example, it is noted in Column 1, lines 39 andfollowing that light dosage values in the range of up to 400 mW/cm² aretypically required for dental applications. On the other hand, a medicalapplication such as photodynamic therapy of psoriasis and basal cellsrequires much lower power typically in the range of up to 100 mW/cm².The device according to the '711 patent includes generally a powersupply, a housing, and a substrate upon which a plurality of lightemitting diodes are mounted. It can be seen from FIGS. 1 and 6 of thepatent that the LED array is generally planar and that the devicetypically includes an optical assembly such as a fiber optic taper. Hereagain, the LED can comprise “blue” LEDs with a spectral emission in the470 nanometer range. Typically, the LEDs are driven by a pulsed powersupply in order to minimize heat generation.

U.S. Pat. No. 5,711,655 to Adam et al. discloses a method and apparatusfor bonding orthodontic brackets to teeth. The subject device includes abase with a central opening and a body with a passage aligned with thatopening. A curing light assembly includes an outer end portion that isremovably received in the passage for curing adhesive beneath thecentral section of the bracket body. Once the adhesive beneath thecentral section of the bracket body is cured to temporarily tack thebracket base to the patient's tooth adhesive extruded from theperipheral edge of the bracket base can be readily removed withoutdislodging the bracket from its intended position. The device can beused to create a temporary “tack” bond while another device is used tofully cure the composition. See Col. 8-9. A curing light assemblyoptionally includes a focusing lens for an LED emitter which may be adome shaped lens that covers the diode. See Column 6, lines 45 andfollowing.

U.S. Pat. No. 6,102,696 to Osterwalder et al. discloses a self-containedlight source for curing light initiated resins used to coat teeth asveneers and fill cavities and chips in teeth in aesthetic or restorativeprocedures. The source includes an elongated container holding a batteryand an electronic compartment in one end and a light emitting window atthe other. A plurality of closely spaced light emitters, typically lightemitting diodes or laser diodes are arrayed in a radial or arcuateconfiguration to direct light to a common focal point. The light isdirected out of the container toward a tooth bearing the resin to becured to a hard stable state. The light emitters produce light in aregion of the spectrum to which the resin curing initiator is sensitive,typically blue light. It can be seen from FIGS. 2 and 3 of the '696patent that LEDs are typically arrayed in an arcuate configuration abouta focal point 38. The apparatus is reported to be useful for curingdental resins including a 1:1 mixture by weight of bis-phenol-2 bis(2-hydroxypropyl) methacrylate and tri (ethylene glycol) dimethacrylatemonomers. The resinous mixture may further include a camphorquinonephotoinitiator and a tertiary amine reducing agent. Fillers such assilica particles and colorants are typically included to achieve thedesired hardness level and color.

U.S. Pat. No. 6,159,005 to Harold et al. discloses an apparatus forphotopolymerizing synthetic materials, specifically dental materialscontaining camphorquinone or phosphine oxide as photoinitiators includesa light source constituted by a semiconductor base solid state radiationemitter which emits in the blue spectral range. Since the radiationemitter emits in a relatively limited spectral range excess heatradiation is avoided. The overall device is formed as a relatively smalllightweight device with a built in battery. The device further includesa light-conducting rod in order to direct radiation to the desiredlocation. According to the '005 patent an essential photoinitiator indental materials is typically camphorquinone or phosphine oxide whichabsorbs a broad band within the blue spectral range, with an absorptionmaximum of about 472 nm and 430 nm, respectively. The patent furthernotes that depending on the color of the material, the polymerizationreaction requires light having an intensity of at least 1 to 5 mW/cm²within a very thin layer. In the practice of polymerizing tooth fillingsor dental replacement parts, a light intensity of at least 250 mW/cm² isrequired within an appropriate period of time to achieve polymerizationof sufficient degree and depth. Commercially available dentalpolymerization apparatuses, at least according to this '005 patent, emitlight at an intensity of about 400-500 mW/cm² sometimes up to 700mW/cm². The solid state radiation emitter according to the '005 patentis preferably a laser diode which emits a forward beam used for thepolymerization proper and a backward beam used as a reference beam forcontrolling the intensity of the polymerization beam.

WIPO Publication No. WO 99/35995 (essentially same as U.S. Pat. No.6,200,134) of Kovac et al. discloses a curing device for curing lightsensitive compounds. The device includes generally a housing and anarray of solid state light emitting diodes for having wavelengths in therange of 400-500 nm. Preferably, a peak wavelength of 470 nm isgenerated. The device further comprises an optical fiber light pipe forcapturing the light and transmitting a beam of the light to the dentalor other work surface containing a light curable compound. An opticallens may be used for focusing the light into the light pipe. It is notedon page 8 of this publication that 200-500 LEDs are used for creatingthe necessary light power needed for curing available dental compounds.In one embodiment of the device described, 96 LEDs are used whereas in aprototype e.g., an embodiment was made wherein 9 LEDs were utilized. Seepage 14. It is further noted in the publication that LEDs which includeintegral lenses may be employed. It should be noted that the LEDsaccording to this publication are generally arranged in a planar array.See, e.g., FIG. 3A. The discussion on page 20 and following notes thatradiated power levels of approximately 200 mW/cm² or greater aregenerally necessary for curing the available dental compounds. Otherintensities may be necessary for curing other light sensitive compounds.Thus the description in the WIPO publication is generally directed tofairly high power levels.

U.S. Pat. No. 5,885,082 to Levy discloses the use of laser radiationhaving a selected wavelength and being in the form of pulses for cuttingbone and performing dental procedures. There is disclosed in Column 4,lines 27 and following a filling material for teeth constituted by amixture formed from a liquid component composed of phosphoric acid andwater and a powder component composed of a ceramic and hydroxyapatite,with the ingredients mixed in a proportion to form a paste having aconsistency such that the paste is workable and sufficiently selfsupporting to be applied to the opening with a spatula and remain inplace. The '082 patent does not involve a photocuring process and thematerial is not a dental polymer composite. The high peak power of thelaser is believed only used for cutting and possibly hardening of thecement due to heat.

BRIEF SUMMARY OF THE INVENTION

Very generally, there is provided in accordance with the presentinvention a device for curing dental compositions and curing methodsthat comprise exposing the dental composition to be hardened toradiation from an axial array of light emitting diodes (“LEDs”) havingoutput wavelengths selected to photo-activate a hardening chemicalreaction within the target composition.

The inventors have surprisingly discovered that relatively low powerradiation from LEDs provides the same depth of cure as achieved by aconventional blue-light filtered dental gun, even though the LEDirradiation intensity is between about 50% to 80% lower for the sameexposure time. In particular, to achieve a 3.0 mm (1.5 mm ISO) depth ofcure with a 60 second exposure time, an energy density of about 25mW/cm² at the target composition is required for an LED-based dental gunvs. an energy density of about 53 mW/cm² required for a conventionalblue-light dental gun. Remarkably, in the instance of a 4.0 mm (2 mmISO) depth of cure with a 60 second exposure, an irradiation intensityof about only 38 mW/cm² at the target composition is required for asingle LED-based dental gun vs. about 200 mW/cm² required for aconventional blue-light dental gun. Here the depth of cure is reportedas the height of the cured cylinder. The ISO method reports the depth ofcure as half the height of the cured cylinder and is sometimes given inparentheses as above and below.

Even more unexpectedly, it has been discovered that the amount ofshrinkage that occurs during the curing process for irradiationintensities yielding a 3.0 mm (1.5 mm ISO) depth of cure in 60 secondsis about 7% lower when a single-LED-based dental gun is employed insteadof a conventional blue light dental gun. In addition, the smaller sizeof an LED permits a smaller dental gun to be employed so that the levelof discomfort experienced by a patient is decreased. Even further, forirradiation intensities yielding a 3.0 mm (1.5 mm ISO) depth of cure in60 seconds, the degree of heating has been measured and found to beabout 9% less when the LED-based dental gun of the present invention isemployed instead of a conventional blue light dental gun. Thus the useof the present invention causes a lower thermal discomfort to thepatient.

For depths of cure higher than 4.0 mm (2 mm ISO) the inventors have findsurprisingly good curing characteristics with an LED gun using fourLEDs. In particular, to achieve a 4.5 mm (2.25 mm ISO) depth of cureunder a 40 second exposure, an energy density of about 180 mW/cm² at thetarget composition is required for the four-LED gun vs. an energydensity of about 450 mW/cm² required for a conventional blue-lightdental gun. Remarkably, for these intensities, a 40 second exposureresults in a temperature rise that is up to 50% lower in the case of thefour LED device as compared to the conventional blue-light dental gun.The amount of shrinkage is about 10% lower than that resulting fromcuring using a conventional dental and the top and bottom surfacehardness obtained using the four-LED device is at least as good as thatobtained with a conventional lamp.

Exemplary LEDs useful in practicing the present invention includePanasonic's “LED Blue Clear” 1500 millicandela T1-¾, LNG992CFBW andsimilar devices commercially available from Hewlett Packard, Toshiba andNichia. Such LEDs emit radiation in the range from about 440 to about500 nanometers with a power output of about 1500 millicandela. Aprogrammable power supply 24 employed in conjunction with the aboveidentified Panasonic LED is well know in the industry; specifically amodel PS 281 produced by Tektronix may be used to obtain the resultsdescribed below. It has also been discovered that LED's may be operatedrelatively close or at their maximum luminous output. For the NichiaLEDs with model number NSPB500S-XF3 the maximum continuous currentspecification is 30 milliamperes with recommended value at 20milliamperes. Pulsed operation with a maximum current at 100milliamperes is recommended only for a maximum duty cycle of 10%. Atthese operating conditions LEDs typically have lifetimes of over 50thousand hours. However in our tests, a Nichia NSPB500S-XF3 was kept“on” for about 10 days continuously at a current of 90 milliamperes withno deterioration in its output. For dental curing applications, the LEDstays on only for about 60 seconds at a time and therefore this highercurrent is not expected to alter the LED output characteristics for alifetime that is comparable to the typical lifetime at recommendedoperating conditions.

Specific exemplary compositions may include: TPH Spectrum composite(shade A3.5) from Dentsply International, Inc. wherein the resin matrixof the composite consists of a BisGMA-adduct (adduct of2,2-Bis[4-2-hydroxy-3-methacryloyloxpropoxy)-phenyl]propane withhexamethylene diisocyanate), ethoxylated Bisphenol-A-dimethacrylate(Bis-EMA, 2,2-Bis[4-(2-methacryloyloxyethoxy)-phenyl]propane) andtriethylene glycol dimethacrylate. The combination of barium aluminoboro silicate glass filler with a mean particle size below 1 μm andcolloidal silica (particle size of about 0.04 μm) results in a hybridcomposite with good strength and wear resistance for posterior use,combined with high surface luster and smoothness, which is an essentialproperty for anterior use of a composite; as well as adhesives includinglight cure resin bond from Reliance which includes Bis-GMA andethoxylated derivative, Polyethylene glycol dimethacrylate amine, Ketonephotoinitiator. Filler particles include 60-99% fused silica and 7-13%amorphous silica. U.S. Pat. No. 5,711,665 suggests the use of asingle-LED for bonding of orthodontic brackets to the tooth surface.However the use of a single LED here is to provide a ‘tack’ bond thattemporarily secures the orthodontic bracket to the tooth. “Subsequently,remaining portions of the adhesive between the bracket base and thetooth are cured by another curing light assembly, possibly emitting agreater intensity of light can be used.” This indicates that the singleLED curing in this patent is intended more for temporarily forming a“tack” bond rather than completely curing the adhesive. Thereforecomplete curing of adhesives is also within the scope of the presentinvention. Surprisingly our tests with the four LED device yields adepth of cure of several mm (typically 4 mm (2 mm ISO) or more) in theadhesives with a 40-60 second exposure, far more than the cure depththat is typically required for the adhesive layer.

There is provided in accordance with the present invention a device forcuring a photosensitive dental composition curable by way of irradiationwith light of predetermined wavelength including as components:

(a) a power supply; and

(b) a radiation source coupled to the power supply and powered thereby,the radiation source having a radiation output and including an axialarray of light emitting diodes, wherein the axial array of lightemitting diodes has a plurality of light emitting diodes mounted aboutan assembly axis defined thereby at a plurality of axial distances fromthe radiation output of the radiation source and being furthercharacterized in that the plurality of light emitting diodes aredirected along a plurality of divergent paths such that a positioninsensitive optical field is generated for curing the dental compositionIn a preferred device, the plurality of light emitting diodes comprises4 light emitting diodes with a first pair of light emitting diodesmounted a first distance from the radiation output of the radiationsource and a second pair of light emitting diodes mounted a seconddistance from the radiation output of the radiation source, the seconddistance being greater than said first distance. The second distance maybe greater than said first distance by from about 0.5 mm to about 2 mm;typically the second distance is greater than the first distance byabout 1 mm.

Each of said light emitting diodes is usually mounted about the assemblyaxis at an angle of from about 10° to about 30°; typically at an angleof about 20°. The device may include a lens, the outer surface of whichlens defines the radiation output of the radiation source. The lens maybe an aspherical lens. So, also, each of the light emitting diodes mayhave a characteristic maximum luminous power output and the power supplymay be adapted to operate each of said light emitting diodes at aluminous power output of at least about 85 percent of its maximumluminous power output.

The position insensitive optical field is generally uniform over anaxial distance of from about 1 to about 5 mm from said radiation outputof said radiation source.

In another aspect of the present invention there is provided a method ofcuring a photosensitive dental composition curable by way of irradiationwith light of predetermined wavelength by way of:

A. applying the said photosensitive dental composition to a dentalsurface, or a cavity; and

B. irradiating the dental composition with a position insensitiveoptical field generated by way of an irradiation source including anaxial array of light emitting diodes, wherein the axial array of lightemitting diodes comprises a plurality of light emitting diodes mountedabout an assembly axis defined thereby at a plurality of axial distancesfrom the radiation output of the radiation source and being furthercharacterized in that the plurality of light emitting diodes aredirected along a plurality of divergent paths.

Still further aspects and advantages of the present invention willbecome readily apparent from the discussion which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail below with reference to the variousfigures wherein like numerals designate similar parts and wherein:

FIG. 1 is a schematic view in perspective showing generally theconfiguration of a compact, hand held photocuring device of preferredclass of the present invention.

FIG. 2 is a schematic view of the device of FIG. 1 provided with aflexible arm illustrating bending and rotation of the LED head assemblyof the device;

FIGS. 3A and 3B are schematic views in section and in elevation (3A) andin section and plan (3B) showing the geometry of a 4-LED head assemblyarranged in an axial array about a symmetry axis, which may be affixedto the device of FIG. 1;

FIG. 4A is a schematic view of a LED head assembly similar to the typeshown in FIGS. 3A and 3B;

FIG. 4B is a schematic diagram showing a portion of an LED head assemblyhaving a single LED;

FIGS. 5A and 5B are partial schematic views in section and elevation(5A) and in section and plan (5B) showing the geometry of a four LEDhead assembly wherein the LEDs are axially arrayed about an axis ofsymmetry defined thereby;

FIG. 6 is a plot of typical LED current vs. LED luminous power outputfor LED's useful in connection with devices and processes of the presentinvention;

FIGS. 7A and 7B illustrate respectively the LED head assembly of FIGS.4A and 4B disposed directly opposed to a target composition and inclinedwith respect to a target composition; and

FIG. 8 is a plot of depth of cure vs. time for the LED head assemblyorientations shown in FIGS. 7a and 7 b.

DETAILED DESCRIPTION

In order to demonstrate the improved dental curing obtained using LEDradiation, comparative tests were completed using an LED dental curingapparatus of the class described generally herein and a conventionaldental radiation curing unit like that available from DentsplyInternational Inc., Caulk Division, Milford, Del., specifically theSpectrum™ Curing Unit, Model 200R. This unit is typical of othercommercially available conventional curing units and employs a quartzhalogen lamp filtered with a blue filter and includes an on-boardradiometer to assure minimum levels of output power. The Model 200Rprovides a minimum operating intensity of about 450 mW/cm² in the400-500 nanometer wavelength range at the output of its light guide.This intensity decreases as distance to the target from the output endis increased.

The initial tests described herein were completed using commerciallyavailable dental compositions; in particular, two different products,the DenMat® Marathon V #5474 and the Caulk TPH Spectrum Shade A 3.5compositions were used to obtain comparative performance data betweenthe LED curing method of the present invention and prior artconventional methods. In the following illustrative tests, twocomparisons are made. In the first comparison the single-LED and dentalcuring apparatus was operated at an energy output level of about 25mW/cm² at the dental composition target 36 and was stationed at adistance of about 7 mm±2 mm above the target 36 for a period of 60seconds. The curing performance of this source is compared to thatobtained using both the four-LED dental curing apparatus and theconventional Spectrum™ 200R Curing Unit applying energy levels of 25mW/cm² and 53 mW/cm², respectively, at the target 36 for a period of 60seconds. In the second comparison a four-LED dental curing apparatusoperated at an about 180 mW/cm² is compared to a conventional curingunit at about 450 mW/cm² for a period of 40 seconds. Variation of lightintensity of the conventional curing unit for these tests was achievedthrough the use of neutral density filters and/or by varying thedistance between the output end and the target composition. In allinstances the actual intensity was determined at the location of thetarget composition using a variable area aperture followed by an opticalpower meter to record the optical power incident on the aperture. Unlessotherwise indicated, all irradiation intensities reported below refer tothe energy applied at the irradiated surface of the dental compositiontarget 36.

(1) Measurement of Depth of Cure

Depth of cure was measured in accordance with the established industrystandard depth of cure measurement technique defined by theInternational Organization for Standardization as ISO DIS 4049; 1998.This technique employs a 7.0 mm thick stainless steel mold having a 4.0mm diameter cylinder that extends through the mold. The thickness of themold is 2 mm greater than twice the maximum depth of cure claimed. Thedental composition to be cured, in this instance, the Caulk TPH SpectrumShade A 3.5 composition, is tightly filled into the cylinder and theopen ends of the cylinder are covered with a polyester film. One end ofthe cylinder is irradiated with curing radiation under test conditionsand then the uncured material is removed from the cylinder. The curedcylinder is removed from the mold and the cured height is measured witha micrometer. The ISO depth of cure is recorded as half the height ofthe cured cylinder and the test is repeated twice. As described above,both radiation sources, the dental curing apparatus 10 and the Spectrum™200R Curing Unit were used to cure the cylinder of dental composition.

Depth of cure for a 4 mm diameter cylinder mold for a 60 second exposurewas then measured and determined to be 3.0±0.2 mm (1.5±0.1 mm ISO depthof cure) for the single-LED radiation and the four-LED curingapparatuses 10 operated at an irradiation intensity of 25 mW/cm². Incontrast, to obtain a similar depth of cure using conventionalblue-light radiation like that emitted from the conventional Spectrum™200R Curing Unit, it was necessary to operate at an irradiationintensity of 53 mW/cm². In the instance of obtaining a 4.0 mm depth ofcure (2.0 mm ISO depth of cure) with a 60 second exposure, thesingle-LED and the four-LED radiation curing apparatuses were operatedat 38 mW/cm² and 50 mW/cm², respectively, and the conventionalblue-light radiation-curing gun was operated at about 200 mW/cm². Toachieve a 4.5 mm depth of cure (2.3 mm ISO depth) under a 40 secondexposure using a four LED head, an irradiation intensity of about 180mW/cm² at the target composition 36 is required for the LED-based dentalgun vs. an irradiation intensity of about 450 mW/cm² required for aconventional blue-light dental gun. Thus, the single-LED and thefour-LED curing apparatus may be operated at a much lower irradiationintensity than conventional dental guns to obtain an essentiallyequivalent or greater depth of cure.

(2) Measurement of Shrinkage

The degree of shrinkage associated with polymerization with a polymerdental composition was measured in accordance with an established ADAHFindustry standard technique using a dilatometer. A dab of dentalcomposition with approximately 0.1 gram mass is placed on a standardmicroscope slide that has been tared on a 4-digit balance. Thecomposition is spread on the slide with a spatula, keeping thecomposition less than 1.5 mm thick and less than 5 mm in diameter toassure complete curing. The weight of the composition is recorded to 4decimals. An open glass measurement tube having a cup-shaped end sectionis positioned with the cup-shaped end section facing upwards and themicroscope slide with the dental composition is inverted over the cup sothat the composition is centered in the cup. The slide is clampedsecured to the measurement tube with a clamp, rotated 180-degrees to thedesired orientation and filled with mercury. A linear displacementtransducer, a Lucas Shaevitz LVDT, assembly is slowly lowered into thetube until it rests on top of the glass measurement tube with itsplunger floating on the mercury. A thermistor (an Omega 44133thermistor) is built into the cup-shaped section of the measurement tubeand positioned to be in contact with the mercury surrounding thecomposition being tested. The LVDT assembly and the thermistor areconnected to a control box (not shown) and interfaced to a computer (notshown). Both radiation sources, the single-LED dental curing apparatusand the conventional Spectrum™ 200R Curing Unit were used to irradiatethe dental composition for 60 seconds at output power levels of thatyield 25 mW/cm² and 53 mW/cm², respectively. In addition, for a 40 sexposure, the 4-LED dental curing apparatus operated at about 180 mW/cm²is compared to the conventional curing unit operated at about 450mW/cm².

A software program developed by the ADAHF residing within the computeris used to acquire and analyze data related to an expansion of themercury from the LVDT and mercury temperature changes registered by thethermistor. The change in mercury level results from two sources: (1)shrinkage in dental composition due to polymerization, and (2) expansionin mercury due to irradiation induced heating. The software programcalculates the expansion in mercury from the thermistor temperaturedata. The overall volume change is calculated based on LVDT data. Fromthe combination of these data, the shrinkage within the dentalcomposition may be calculated once the final density of cured polymer isprovided. Final density of the polymer is measured using a MettlerToledo AT 261 balance in combination with a Mettler Toledo 210485density determination kit.

(3) Measurement of Heat

The increase in temperature associated with a 60-second exposure forachieving a depth of cure of 3.0 mm (1.5 mm ISO depth of cure) wasmeasured using the ADAHF dilatometer described above. Again, the dentalcuring apparatus and the conventional Spectrum™ 200R Curing Unit wereused to expose dental composition target for 60 seconds at irradiationintensities measured to be 25 mW/cm² for the single-LED and the four-LEDcuring apparatus and 53 mW/cm² in the case of the conventionalblue-light dental gun. In addition, temperature rise was compared for a40 second exposure from a four-LED curing apparatus operated at about180 mW/cm² to a conventional curing apparatus operated at about 450mW/cm².

The dental curing apparatus using an LED produced an initial temperatureincrease of about 0.8° C. whereas in contrast the conventional lightSpectrum™ 200R Curing Unit produced an initial temperature increase ofabout 0.9° C. Thus the single-LED dental curing apparatus 10 producedlower overall heating of the composition in contrast to the higheroverall heating from the conventional blue light curing unit. Thereby,when treated with the dental curing method of the present invention, apatient will experience a significantly lower degree of discomfort as aresult of the about 8% lower temperatures during curing of an embeddeddental composition with a single-LED device. A 40 second exposure ofradiation from the four-LED device at about 180 mW/cm² yields atemperature rise of up to 50% lower than the conventional curing unitoperated at about 450 mW/cm².

Shrinkage measurements made using these same irradiation intensities,which yield a 3.0 mm depth of cure (1.5 mm ISO depth of cure), showedthat the single-LED dental curing apparatus of the class of the presentinvention operating at 25 mw/cm² produced a shrinkage of 2.8% whereas incontrast the conventional Spectrum™ 200R Curing Unit operating at 53mW/cm² produced a shrinkage of about 3.0%. A 40 second exposure ofradiation from the four-LED device at about 180 mW/cm² yields about 2.2%shrinkage in the composite, while the conventional curing unit operatedat about 450 mW/cm² yields a shrinkage of 2.5%.

(4) Measurement of Hardness:

Hardness measurements were performed on a dental composition cured witha convention curing lamp and the four-LED device using a standardhardness tester (Barber-Coleman Impressor Model No. GYZJ 934-1). Thecomposition was slightly over-filled into a stainless steel mold with adiameter of 5 mm and a thickness of 2 mm. The two open ends of the moldwere covered with polyester film and the mold was pressed between twoglass plates to firmly pack the composite in the mold. The mold wasirradiated for 20 seconds using three comparative sources: Aconventional curing unit operated at about 450 mW/cm² was compared to afour-LED apparatus operated at about 180 mW/cm². The composition usedwas the Heliomolar Radiopaque® Shade A3. For both these sources the topsurface hardness is about 60 while the bottom surface hardness ismeasured to be about 53 on the Barber-Coleman hardness scale.

(5) Failure Mode

Although actual results were not experimentally determined, it is wellknown within the industry that dental curing guns employing conventionalradiation sources gradually lose power output during the life of thedental gun. For example, a negative correlation between the depth ofcure and the age of light-curing guns has been reported, with olderHeliotests (Ivoclar-Vivadent) units tending to cure a Z100 Composite(3M) dental composition to less depth than newer units [Prim Dent CareSep. 4, 1997 (3): 91-4]. Because of this time loss of power output,curing lights are considered as unsuitable for use with a reading ofless than 200 mw/cm² using a curing radiometer and greater than 50mw/cm² using a heat radiometer [J Dent Mar. 27, 1999 (3): 235-41]underscoring the necessity of monitoring the output of conventionaldental curing guns as they age in use. In contrast, an inherentcharacteristic of LED radiation sources like those used in the presentinvention is a stable level of output radiation during the operatinglife of a LED, with a catastrophic failure that is readily noticeable byan operator whenever the output declines.

(6) Relative Costs

The expenses associated with conventional radiation dental curing gunscomes about as a result of the need to provide relatively high outputpower with appropriate filtering and cooling means. Such guns and theassociated power supply cost in the $600-1,000 range. In contrast, theLED-base dental curing method of the present invention employs low powerLEDs costing in the $5 range per LED ($20 for a four-LED head) and notrequiring the high output power, filtering and cooling means ofconventional dental curing guns.

The following Table 1 contains the results of preliminary testing in acondensed form. The advantages of using LED curing are evident.

TABLE 1 Comparison of Curing Performance New LED Prototype with:Conventional Single LED Four LED Curing Radiation Source Head Head LampPower density at the target composition [2] [2] (Caulk TPH SpectrumShade A3.5) that achieves a cure depth [1] of: 3.0 mm (60-s exposure) 25mW/cm²  25 mW/cm²  53 mW/cm² 4.0 mm (60-s exposure) 38 mW/cm²  50 mW/cm²200 mW/cm² 4.5 mm (40-s exposure) 38 mW/cm² 180 mW/cm² 450 mW/cm² (3.7mm) [3] Temperature rise in target composition (Caulk TPH Spectrum ShadeA3.5) for irradiation that achieves a cure depth of: 3.0 mm (60-sexposure) 0.8° C. 0.8° C. 0.9° C. 4.5 mm (40-s exposure) 0.8° C. 1.0° C.1.8° C. (3.7 mm) [3] Shrinkage in composite (Caulk TPH [9] [9] [9]Spectrum Shade A3.5) for irradiation that achieves a cure depth of: 3.0mm (60-s exposure) 2.8% 2.9% 3.0% 4.5 mm (40-s exposure) [8] 2.2% 2.5%(3.7 mm) [3] Beam Divergence ˜6 degrees Negligible ˜27 degrees [4]Relative Cost of Light Source ˜$5 ˜$20 ˜$100 Minimum cure time forHeliomolar NA 23 s 25 s Shade A3 [5] Depth of cure/Top surface hardness[7] achieved with a 40 s exposure at optimum operating power [6]: CaulkTPH Spectrum Shade A3.5 3.7 mm/63 5.1 mm/63 4.5 mm/69 Kerr Prodigy ShadeA3.5 3.0 mm/51 4.1 mm/55 4.5 mm/69 Top/bottom surface hardness of a 5 mm[8] 60/53 60/53 diameter, 2 mm thick cured piece of Heliomolar shade A3at 20 s cure time. Autoclavable Replaceable Replaceable Yes (tip)protective protective sheath sheath Minumum life expectancy athigher >40,000 >40,000 Typically currents used for this applicationquoted in the (estimated number of 60-second curing few thousandsoperations) [10] Degradation with time None until None until Continualcatastrophic catastrophic degradation failure failure with timeRadiometer Requirement NO NO YES [1]- Cure depth is defined as theheight of the cured cylinder of composite resin. To obtain depth of cureas defined in the ISO method, this height needs to be divided by two.[2]- It was shown by Pradhan, Melikechi and Eichmiller in the JournalDental Materials that the cure depth is higher when the spectralemission profile of the source matches the spectral absorption peak ofthe photo-initiator in dental composite resins. This being the case, theLED based devices can match the curing performance of the conventionalcuring lamp at a much lower irradiation power density. [3]- A Single-LEDhead operated under optimum operating conditions yields a cure depth of3.7 mm with a power density of ˜38 mW/cm². Higher depth of cure requiresthe use of the Four-LED Head. [4]- The unique Four LED geometry achievesuniform intensity over a distance of 5 mm from the head and this amountsto negligible beam divergence over the operating distance. [5]- Minimumcuring time is defined as the time required to achieve a hardnessmagnitude at the bottom surface of a 2 mm thick cured piece that iswithin 90% of the hardness magnitude at the top surface. [6]- 38 mW/cm²for the Single-LED Head, 230 mW/cm² for the Four-LED head and 450 mW/cm²for the conventional curing lamp. [7]- Hardness in Barber-ColemanHardness Scale. For comparison, typical readings of Aluminum alloysrange from a minimum of 35 to a maximum of 85 on the Barber Colemanscale. [8]- The single-LED head is not suitable for deep curing. Afour-LED head is therefore recommended. [9]- The estimated uncertaintyon the shrinkage measurements is ±8% of the reported shrinkage, which isclose to ±0.2%. [10]- Plasma ark sources probably have a lifetime thatis comparable to the LEDs but they require several hundreds of dollarsto replace. NA- Not applicable

It is to be understood that the specific embodiments of the inventiondescribed herein are illustrative of the principles of the invention andthat other modifications may be employed which are still within thespirit and scope of the invention. For example, in one alternateexemplary embodiment, a dental composition having a differentformulation from those noted above may be employed. It is known from theliterature that Axis and Thermoresin LC II dental compositions may becured with both UV and visible radiation while another compositionDentacolor is cured substantially by visible light [J Oral Rehabil Oct.25, 1998 (10): 770-5]. To confirm the effectiveness of LED curing, thedepth of cure of a second commercially available dental compositionknown as Marathon V available from DenMat® was also evaluated using anLED-based curing method in the aforedescribed ISO DIS 4049 testingmethod. The test results were essentially a duplicate of those reportedin the above. It was shown that the single-LED method provides arelatively constant depth of cure as long as the LED is positionedwithin a distance of 8 mm from the dental composition, a result of thelow divergence of the LED beam in comparison to the highly divergentradiation generated within a conventional filtered light dental gun.Optimum distance from the dental composition target is seen to be in therange of 1-8 mm for the single-LED curing devices and methods describedherein. The unique geometry of the four-LED device provides optimumperformance at a distance of 1-5 mm from the dental composition target.

In another embodiment, a light emitting diode having other than “clearblue” wavelengths may be employed as long as the dental composition maybe cured by the application of corresponding radiation. It is known fromthe literature that microfilled and hybrid composition materialsdesigned for prosthetic veneer may be cured with different types oflight, in particular both xenon light and metal halide light sources.Depending on the choice of light source and the choice of dentalcomposition, an increased exposure duration increases the depth of curefor all combinations [J Oral Rehabil May 25, 1998 (5): 348-52].Accordingly the present invention may be practiced using any LED havingits wavelength selected to provide radiation energy in the effectivecuring range for the composition being employed. In this alternateexemplary embodiment, the duration of radiation exposure with a LED asdisclosed in the present application may be increased to accomplish aminimum acceptable depth of cure, depending on the selection of LEDradiation wavelength and the selection of dental composition.

Referring to FIGS. 1 and 2 there is provided a hand held curing device10 which includes a handle 12 adapted for gripping by a user as well asa compact LED mounting head assembly 14 attached to the handle by way ofa flexible arm 16. Arm 16 may be of the “gooseneck” type, made up of aplurality of annular segments such that it can rotate or bend to atemporarily fixed position.

There is further provided a power supply 18, which typically includes atransformer, connected to the mounting head assembly by way of a powercord 19 including wires 20, 22 in order to power the LEDs mountedherein. Power cord 19 is preferably of the retractable type as is wellknown. Alternatively, the device may be battery powered as is also knownin the art.

In FIG. 1, arm 16 is in a coaxial configuration with handle 10, that is,both arm 16 and handle 12 are aligned along a device axis 24 in astraight line. In a preferred embodiment, a head assembly mounting axis26 has a head assembly mounting angle 28 between axes 24, 26 of fromabout 40° to about 80° and preferably about 60° as is shown in theFigures. There is optionally provided a removable sheath 30 to cover thedevice, which may be changed between uses of the device and preventcross contamination between patients. Sheath 30 is generally constructedof polymer film.

It is shown in FIG. 2 that the compact LED mounting head assembly may besuitably positioned by bending, wherein axis 24 becomes bent, orrotating about axis 24 as indicated by arrow 32. The inventive devicealso provides for adjusting the direction of the output path ofradiation indicated generally at 34 by way of a lens or the position ofthe LEDs within compact head 14 as further discussed herein. Theforegoing combination of features makes the device readily adjustable sothat it may be used to irradiate a target composition indicated at 36 ina fully optimized manner.

Likewise, an important feature of device 10 is the compact size of headassembly 14. In accordance with the invention, head 14 may have a height38 of 10-20 mm, preferably about 15 mm and a diameter 40 also of about10-20 mm, preferably about 15 mm.

FIGS. 3A and 3B illustrate a four LED compact mounting head assembly 14useful for mounting on device 10. FIG. 3A is a schematic view along thecenterplane of assembly 14 showing three LEDs, 42-46, whereas FIG. 3b isa top plan partial schematic view of the assembly 14 of FIG. 3a, showingall four LEDs 42-48. Compact mounting head assembly 14 includes a top 49and a sidewall 50 and is configured for housing and optionally mountingLEDs 42-48 which communicate with the power supply via wires 20, 22through arm 16. The LEDs are mounted such that the LEDs may be suitablypositioned with respect to a target composition indicated at 36 at adistance 52 from the output of LED head assembly 14. Distance 52 issuitably from about 1-8 mm and preferably about 4 mm. The LED headsshown in FIGS. 3A through 4B generate an optical field that isrelatively position insensitive and optimal curing results can beachieved over a variety of distances, as further discussed below.

Head assembly 14 of FIGS. 3A and 3B includes a single convergent lens 54which may be an aspheric lens. In the device shown, distance 52 ismeasured from the center of outer surface 56 to target composition 36.LEDs 42-48 are arranged in an axial array about an axis of symmetry 58wherein LEDs 46, 48 are mounted directly on lens 54 and LEDs 42, 44elevated above lens 54 a distance 60 and are thus further from theoutput of the head assembly 14 (in the case shown in FIGS. 3A and 3Bouter surface 56 of lens 54) by that amount. In other words, LEDs 46 and48 are mounted at a first distance form the output of the device andLEDs 42, 44 are mounted a second distance, greater than the firstdistance from the output of the device; the difference being distance60. Distance 60 is generally from about 0.5 mm to about 2 mm with about1 mm being typical.

Each LED has an axis such as axes 62, 64 of LEDs 42, 44 which make anangle 66 with assembly axis of symmetry 58 as shown. Angle 66 may varybetween LEDs and is typically between about 10° to 30° with about 20°being preferred.

Thus, arranged in an axial array, LEDs 42-46 define a plurality ofdivergent radiation paths thereby generating a position insensitiveoptical field for curing composition 36. As used herein, the terminology“a plurality of divergent radiation paths” means and includesarrangements where all of the LED are not directed to a single commonfocal point; whereas the terminology “axial array” refers to the factthat at least two LEDs are located at different distances from theoutput. In the embodiment shown in FIGS. 3A and 3B LEDs 42, 44 areangled such that their outputs (along axes 62, 64) are directed atcommon focal point 68 whereas LEDs 46, 48 are directed to focal point70. In yet other embodiments the LEDs are arranged about an assemblyaxis such that there are no focal points common to any two LEDs.

FIG. 4A is an alternate embodiment of the arrangement of FIGS. 3A and 3Bwherein adjacent LEDs 72, 74 touch the lens and two rearward LEDs (notshown) are elevated a distance 60 of 1 mm. Here again, head mountingangle 28 is suitably 60° and the angle 66 between assembly axis 58 andthe axes 74, 76 of LEDs 72, 74 is 20°. The compact dimensions of device10 are further appreciated from FIG. 4A. Lens 54 has a thickness 80, forexample, of about 5 mm at its thickest point whereas the inclined LEDshave a height 82 of about 8.5 mm. The overall height 38 of the LED headassembly is thus 15 mm or less. In a single LED embodiment shown in partin FIG. 4B, a single LED 84 replaces the axial array of LEDs shown inthe various Figures. Single LED 84 has an axis 86 which preferably makesan angle 28 of about 60 degrees with axis 24 of device 10. A single LEDhead assembly 14′ may be employed when it is desired to minimize theoverall dimension of head 14. Thus, head assembly 14′ may be madeinterchangeable with four LED head assembly 14 such that either LED headassembly may be releasably connected to arm 16 by way of plug meansindicated at 88, 90 whereby the head assemblies are mechanically andelectrically coupled to arm 16 and thus handle 12.

In FIGS. 5A and 5B there is shown an arrangement wherein the LEDs aremounted “off axis” of lens 54. Lens 54 has an axis 92 defined by itsfocii 94, 96 as shown in FIG. 5A. Lens 54 is mounted as in FIGS. 3A, 4Ain a housing generally indicated at 14″. LEDs 98, 100, 102 and 104 aremounted as shown in FIGS. 5A and 5B adjacent to lens 54, wherein theyform an axial array about LED assembly axis 58 as described above. Here,however, axis 58 is not coincident with head assembly mounting axis 26in the configuration shown in FIGS. 5A and 5B, where axis 92 of lens 54may be coincident with the axis of the head generally if so desired. Theaxial assembly of LEDs about assembly axis 58 is laterally offset fromaxis 92 by a distance indicated at 106. This distance is the distancefrom the geometric center of the top of the LED closest to the axis oflens 54. Axis 58 is also angularly offset from axis 92 by an angle 108;typically from about 10° to about 50°. It should be appreciated that theangle from radiation emitted by LEDs 98-104 generally follows thedirection of axis 58 but is refracted toward the axis of lens 54 fromits outer portions. Note from FIG. 5B which is a view along the line5B—5B of FIG. 5 and that the LEDs are concentrated on one side of thelens, on the portion of the head closer to handle 16. In thisconfiguration, convergent lens 54 serves the dual functions of focusingthe light and directing it outwardly toward a hard to reach target 36.Moreover, the path can be adjusted either by way of distance 106 orangle 108.

FIG. 6 is a characteristic plot of LED current versus luminous poweroutput for LEDs useful in the devices of the present invention. Suchdevices have a characteristic maximum luminous power output 110 whereincreasing the current does not increase the optical power output. Ithas been found such devices are advantageously operated in connectionwith curing dental compositions at an optical power output of at leastabout 85% of their characteristic maximum luminous power output asindicated at 112 on FIG. 6. The preferred current operating range isshown as the shaded area on FIG. 6 which may be 90, 95 or 100 percent ofthe maximum luminous power output of the device.

The curing device is further appreciated by considering FIGS. 7A, 7B andFIG. 8. In FIG. 7A, a four LED head assembly 14 as described above withan axial array of LEDs is located directly above a target composition36, wherein in FIG. 7B head 14 has been rotated 30° off of axis 114. InFIG. 8, the cure depth versus time is compared for the two orientations.There is virtually no difference in cure depth versus time until curedepths of over 4.5 mm indicating the position insensitivity of theoptical field generated and the overall effectiveness of the device.

Some salient points of this invention and related inventions forming thesubject matter of patent filings contemporaneous with this applicationis the compactness made possible by a unique combination of features.Although it is within the skill of one knowledgeable in the art to use alarge number of LEDs to obtain a desired depth of cure with a specifiedtime (e.g. 3 millimeters within 60 seconds), it is a challenge to obtainthe same performance with a reduced number of LEDs. This reduction,however, is necessary to make the assembly of LEDs compact. Out workshows that the we can minimize the number of LEDs for a desiredperformance and gives surprisingly good results. This is achieved bydoing the following in combination:

a) Driving the LEDs with a non-traditional current-In existingtechnologies the LEDs used are driven at a specifications provided bythe LED manufacturers. The current invention operates an LED at anoptimum and non-traditional operating current 70 that is well beyond thetypical specifications of the manufacturer. Under these conditions, ourtests surprisingly indicate no detrimental effects on the LED used inthe manner indicated for the current invention. The current inventionutilizes a powerful LED 34, with at least the output of an LED like theNichia NSPB500S-XF3;

b) Novel and Unique geometry of the LED head—The novel geometry yieldssurprising intensity and uniformity of irradiation of the material to becured. Our data shows excellent results in terms of the speed of cure,the depth of cure, the hardness and the uniformity of cure. The deviceis to be positioned at a distance of 4.0 mm from the curing site foroptimal curing performance but the design surprisingly allows thisoptimal distance to vary anywhere from 1.0 to 5.0 mm without appreciablyaffecting the curing performance. This 4.0 mm allowed variation in thedistance between the output end of the head and the curing site istypically the maximum variation possible with the mouth fully open.

The novel geometry consists of a combination of a minimal number ofLEDs. In one preferred embodiment the combination consists of four LEDs.The axis of each LED is optimally oriented from the axis of the four-LEDcombination at an angle. A single lens and optimal elevation of LEDs asdescribed above and further noted below are further unique features ofthe compact device.

The single aspheric lens shown in FIG. 3A and following is a novelfeature in this design that efficiently collects light from thecombination of LEDs and delivers maximum light intensity at the curingsite. Any other conveniently shaped convergent lens such as acylindrical lens and other custom built lenses that will efficientlycollect light from any combination of LEDs for efficient curing.

Traditionally a lens is used on-axis for the purpose of focusing. Ourstudy shows that the single lens can be used off-axis in anon-traditional manner to achieve desired results. With appropriateorientation angle and position of the LED assembly axis with respect tothe axis of the lens, the direction at which light emerges from the headcan be varied to reach locations in the mouth that are otherwise hard toreach (see FIG. 5A).

An elevated LED Architecture achieves axial uniformity of radiation.This feature of the device results in a surprising axial uniformity ofthe curing irradiation, generating a position insensitive optical field.The distance of the LED head from the curing site can waiver when thepractitioner holds the device in hand. The great advantage of thisfeature is that the exact distance between the head and the curing sitecan waiver up to several millimeters without affecting the curingperformance. Each LED in the LED combination can be individuallyelevated to a distance from the surface of the lens. In a preferredembodiment two diametrically opposite LEDs in a four-LED combination canbe slightly elevated to a convenient distance from the surface of thelens. No attempt is made to focus the light from the LEDs to a singlepoint. On the contrary, focusing at a single point is to be avoided soas to decrease the sensitivity of the curing characteristics to theexact distance between the head and the curing site. In this respect, aplurality of divergent paths of radiation are preferred

Complementing the above aspects are:

Compactness—The entire LED head is contained in a head that has maximumdimensions of about 15×17 mm. This should allow convenient positioningof the head over the oral curing site. The connection between the headand the power supply can be a thin arm, which needs to carry a thin wirerated for carrying the <500 milliamperes current to the LED assemblyhead, can be as thin as 3-5 mm in diameter.

Transformer—for the current device, no specific attempt is being made tomake it self-contained but it can be so. In one embodiment of the devicethere will be no rechargeable batteries. A thin cable that is longenough for dental usage will connect the handle to the powersupply/transformer to provide the necessary power to the LED head.Rechargeable batteries are expected to hamper commercialization of adevice embodiment due current requirements. With 4-LEDs running at themanufacturer's specifications and without the aspheric lens the lightintensity is expected to be too weak to efficiently cure the dentalresin. With a larger number of LEDs the current becomes a problem. Useof a transformer relaxes these constraints and allows the optimumcurrent to be delivered to the head for as long as it is desired.

Flexible gooseneck arm—As shown in FIG. 2, the arm connecting the LEDhead to the handle can be as thin as 3-5 mm and can, in the preferredembodiment, be a “gooseneck” arm that can be bent and/or rotated toposition the LED head at the desired orientation. The head itself can beattached to the arm at a convenient angle and can be rotated about theaxis of the arm.

Flat printed circuit board—The LEDs will be held at the specified angleby direct bonding onto the lens or by an appropriate socket designed tofit inside the LED head. The device will use a flat printed circuitboard.

Protective sheath—The compactness of the device allows for a protectivelayer or sheath of various kinds to be placed covering the head and thearm between patients to prevent cross contamination. The protectivesheath could be a cap that fits directly over the head or an elasticmembrane that can be stretched over the device. In one embodiment, thelens itself could be a part of a molded piece that can be disposed aftereach patient.

While the invention has been fully described in the context ofparticular embodiments, modifications to such specific embodimentswithin the spirit and scope of the present invention will be readilyapparent to those of skill in the art. The invention is defined in theappended claims.

What is claimed is:
 1. A device for curing a photosensitive dentalcomposition curable by way of irradiation with light of predeterminedwavelength comprising: (a) a power supply; and (b) a radiation sourcecoupled to said power supply and powered thereby, said radiation, sourceincluding an axial array of light emitting diodes and having a generallyplanar common radiation output, wherein said axial array of lightemitting diodes comprises a plurality of light emitting diodes mountedabout an assembly axis defined thereby at a plurality of axial distancesfrom said radiation output of said radiation source and being furthercharacterized in that said plurality of light emitting diodes aredirected along a plurality of divergent paths through said generallyplanar common radiation output wherein at least two of said lightemitting diodes are disposed such that their outputs are along pathswhich intersect at a first focal point and wherein further there is atleast a third additional light emitting diode whose output is along apath which avoids said first focal point such that the plurality ofdivergent paths cooperate to generate a position insensitive opticalfield for curing said dental composition.
 2. The device according toclaim 1, wherein said plurality of light emitting diodes comprises 4light emitting diodes.
 3. The device according to claim 1, wherein saidplurality of light emitting diodes includes a first pair of lightemitting diodes mounted a first distance from said generally planarcommon radiation output of said radiation source and a second pair oflight emitting diodes mounted a second distance from said generallyplanar common radiation output of said radiation source, said seconddistance being greater than said first distance.
 4. The device accordingto claim 3, wherein said second distance is greater than said firstdistance by from about 0.5 mm to about 2 mm.
 5. The device according toclaim 4, wherein said second distance is greater than about said firstdistance by about 1 mm.
 6. The device according to claim 3, wherein eachof said light emitting diodes is mounted about said assembly axis at anangle of from about 10° to about 30°.
 7. The device according to claim6, wherein each of said light emitting diodes is mounted about saidassembly axis at an angle of about 20°.
 8. The device according to claim1, further comprising a lens, the outer surface of which lens definessaid generally planar common radiation output of said radiation source.9. The device according to claim 8, wherein said lens is an asphericallens.
 10. The device according to claim 1, wherein each of said lightemitting diodes has a characteristic maximum luminous power output andsaid power supply is adapted to operate each of said light emittingdiodes at a luminous power output of at least about 85 percent of itsmaximum luminous power output.
 11. The device according to claim 1,wherein said position insensitive optical field is generally uniformover an axial distance of from about 1 to about 5 mm from said radiationoutput of said radiation source.
 12. The device according to claim 1,wherein said plurality of light emitting diodes comprises 4 lightemitting diodes such that a first and second light emitting diode areeach disposed such that their outputs are along paths which intersect ata first focal point and further there are third and fourth lightemitting diodes whose outputs intersect at a second focal point.
 13. Amethod of curing a photosensitive dental composition curable by way ofirradiation with light of predetermined wavelength comprising: applyingsaid photosensitive dental composition to a dental surface, or a cavity;and irradiating said dental composition with a position insensitiveoptical held generated by way of an irradiation source including anaxial array of light emitting diodes, wherein said axial array of lightemitting diodes comprises a plurality of light emitting diodes mountedabout an assembly axis defined thereby at a plurality of axial distancesfrom a generally planar common radiation output of said radiation sourceand being further characterized in that said plurality of light emittingdiodes arc directed along a plurality of divergent paths through saidgenerally planar common radiation output of said radiation sourcewherein at least two of said light emitting diodes are disposed suchthat their outputs are along paths which intersect at a first focalpoint and wherein further there is at least a third additional lightemitting diode whose output is along a path which avoids said firstfocal point such that the plurality of divergent paths cooperate togenerate a position insensitive optical field.
 14. The method accordingto claim 13, wherein said plurality of light emitting diodes includes 4light emitting diodes.
 15. The method according to claim 13, whereinsaid plurality of light emitting diodes includes a first pair of lightemitting diodes mounted a first distance from said generally planarcommon radiation output and a second pair of light emitting diodesmounted a second distance from said generally planar common radiationoutput of said radiation source, said second distance being greater thansaid first distance.
 16. The method according to claim 15, wherein saidsecond distance is greater than said first distance by about from 0.5 mmto about 2 mm.
 17. The method according to claim 16, wherein said seconddistance is greater than said first distance by about 1 mm.
 18. Themethod according to claim 15, wherein each of said light emitting diodesis mounted at an angle of from about 10° to about 30° to said assemblyaxis.
 19. The method according to claim 13, wherein said radiationsource includes a lens, the outer surface of which defines the radiationoutput of said radiation source.
 20. The method according to claim 19,wherein said lens is an aspherical lens.
 21. A device for curing aphotosensitive dental composition curable by way of irradiation withlight of predetermined wavelength comprising: (a) a power supply; and(b) a radiation source coupled to said power supply and powered thereby,said radiation source including an axial array of light emitting diodesand having a generally planar common radiation output and wherein saidaxial array of light emitting diodes comprises a plurality of lightemitting diodes mounted about an assembly axis defined thereby at aplurality of axial distances from said generally planar common radiationoutput of said radiation source and being further characterized in thatsaid plurality of light emitting diodes are each mounted and fixedrelative to a head assembly about said assembly axis at an angle so asto be directed along a plurality of divergent paths through saidgenerally planar common radiation output wherein at least two of saidlight emitting diodes are disposed such that their outputs are alongpaths which intersect at a first focal point and wherein further thereis at least a third additional light emitting diode whose output isalong a path which avoids said first local point such that the diodescooperate to generate a position insensitive optical field for curingsaid dental composition.
 22. A device for curing a photosensitive denialcomposition curable by way of irradiation with light of predeterminedwavelength comprising: (a) a power supply; and (b) a radiation sourcecoupled to said power supply and powered thereby, said radiation sourceincluding an axial array of light emitting diodes and having a generallyplanar common radiation output, wherein said axial array of lightemitting diodes comprises a plurality light emitting diodes mounted andfixed relative to a head assembly about an assembly axis defined therebyat a plurality of axial distances from said radiation output of saidradiation source and being further characterized in that said pluralityof light emitting diodes are directed along a plurality of divergentpaths through said generally planar common radiation output wherein atleast two of said light emitting diodes are disposed such that theiroutputs are along paths which intersect at a first focal point andwherein further there is at least a third additional light emittingdiode whose output is along a path which avoids said first focal pointsuch that the plurality of divergent paths cooperate to generate aposition insensitive optical field for curing said dental composition.23. A method of curing a photosensitive dental composition curable byway of irradiation with light of predetermined wavelength comprising:applying said photosensitive dental composition to a dental surface, ora cavity; and irradiating said dental composition with a positioninsensitive optical field generated by way of an irradiation sourceincluding an axial array of light emitting diodes, wherein said axialarray of light emitting diodes comprises a plurality of light emittingdiodes mounted and fixed relative to a head assembly about an assemblyaxis defined thereby at a plurality of axial distances from a generallyplanar common radiation output of said radiation source and beingfurther characterized in that said plurality of light emitting diodesare directed along a plurality of divergent paths through said generallyplanar common radiation output of said radiation source wherein at leasttwo of said light emitting diodes are disposed such that their outputsarc along paths which intersect at a first focal joint and whereinfurther there is at least a third additional light emitting diode whoseoutput is along a path which avoids said first focal point such that theplurality of divergent paths cooperate to generate a positioninsensitive optical field.